Electromagnetic radiation reflector

ABSTRACT

A reflector (3) may be mounted in a hollow housing (2) adapted to fly in ambient air. The reflector device (3) may be formed from a coating on the surfaces of blocks, the coating being metal or dielectric. Reflecting surfaces whether self supporting or not may be formed as intersecting circles or polygonal (more than four sides). They may be suspended in housing (2) adapted to fly either directly or indirectly by means of an intermediate body within the housing.

BACKGROUND OF THE INVENTION

Reflectors providing a substantially uniform response in all directionshave been made from three mutually orthogonal plates of metal. Theplates may intersect along a centre line. In order to withstand exposureto weather, the metal has to be of substantial thickness and so thereflector is heavy which is inconvenient, particularly for example whenthe reflector is desired to be hoisted to the masthead of a sailingdinghy.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided areflector comprising reflecting surfaces arranged in mutually inclinedplanes, the surfaces being formed on blocks of lightweight supportmaterial. The surfaces are preferably mutually orthogonal. The supportmaterial blocks are secured together with a metallic or dielectriccoating on at least one of the facing surfaces, so that the reflectingcoatings are not exposed to the weather. Complete protection can beachieved by encapsulating the block assembly and the capsule can providemeans for suspending the reflector from a support. The thickness of thecoating has only to be sufficient to act as a reflector and not to beself supporting.

In the prior art, reflectors where the metalized surfaces were selfsupporting and in the form of metal plates, the plates were diamondshaped. Whether the metalized surfaces are self supporting or not, wehave discovered that by making the shape of individual metalizedsurfaces circular or at least closely approximating circular (e.g.polygonal with the number of sides exceeding 4) shape, an improvedresponse is achieved.

According to another aspect of the invention there is provided areflector comprising a plurality of mutually inclined surfaces, each ofwhich extends on either side of lines in which it intersects anothersuch surface, and has a circular or polygonal (with more than foursides) shape.

Although this reflector is light in weight, the blocks of supportmaterial are bulky. We have discovered that it is possible to supportthe metalized surfaces on elements within an inflatable envelope. Theenvelope is stored deflated and then expanded for use by air or anothergas into a spherical shape then internal metalized elements within theenvelope then provide the reflecting surfaces. Thus according to anotheraspect of the invention, there is provided a reflector comprising aplurality of mutually inclined surfaces, each of which extends on eitherside of lines in which it intersects another such surface, and thesurfaces are elements mounted within an expandable envelope. Theelements may be made of wire mesh or textiles and may include stretchfabrics in order to provide reduced resistance to the expansion of theenvelope. In each case, the elements will be coated with metal,preferably silver.

The envelope can be inflated with air to a density of less than unity soit will float. Such reflectors can be thrown overboard from a vessel inorder to provide a dummy reflector on the surface of the sea.Alternatively, a lighter gas can be used to inflate the envelope so thatthe reflectors will float in the air, either freely or tethered to avessel to provide a desired pattern. The tethered reflectors can bereturn to the vessel when they have served their purpose. The envelopescan be deflated and stored flat for re-use.

Although the elements may be mounted directly to the envelope, it ispreferable that they are secured indirectly to the envelope by beingsecured directly to an intermediate body which is mounted within theenvelope.

In one example, the intermediate body is initially formed as a tube withopen ends. This allows the elements to be inserted into the tube fromone end and secured to its interior wall by any suitable means, such asclamping or stapling as well as by glueing. The ends of the tube arethen closed and the tube is mounted within the main envelope. The tubeand the envelope are inflated so that the tube changes from asausage-shape (a cylinder with closed ends) to approximately a sphericalshape as its central portion is expanded by inflation. The tube may beof slightly permeable material so that some of the inflating gas (suchas helium) can escape through the walls of the tube to inflate theenvelope or a separate port may be provided for inflation gas to enterthe space between the tube and the envelope.

After inflation, the tube and the envelope approach each other inapproximately spherical shape and the elements within the tube are drawnout to their intended final arrangement to provide a reflector ofuniform all-around response. The inflated tube and envelope are thenvulcanised so that they stick together. A suitable material for theenvelope is a rubbery material. The tube should be of the same or atleast a compatible material so that vulcanisation can take place.

The reflectors can be inflated so that they float in the air. Theenvelopes can be tethered so that the reflectors float at apredetermined height, thus providing a dummy target at that height,which is selected to be the height of the target the missile directingsystem is expecting. A dummy reflector left to float on the sea surfacedirectly mounted to a floating raft might be rejected by the missiledirecting system, since the system may be programmed to only selecttargets which ressemble, for example, frigates whose vulnerable area(the engine room for example) target height will be many meters abovethe sea surface. A dummy reflector tethered at a height above a floatingraft would not be rejected by such a missile system and so would besuccessful in causing the missile system to believe that it has found agenuine target.

According to another aspect of the present invention, there is provideda reflector for incident electromagnetic energy, comprising a hollowhousing adapted to fly in ambient air and, interiorly thereof, areflector device for reflecting incident electromagnetic radiation.

The housing may suitably comprise an envelope inflatable with a suitablegas.

The reflector device may comprise a substantially spherical device.

There may be a plurality of discrete spherical reflector devices housedin the housing, for example, three.

Each reflector device may comprise an aluminized cloth which is elasticand in the shape of a sphere.

There may be means to position each reflector device within of thehousing.

The positioning means may comprise a plurality of separate connectorswhich extend substantially over the entire surface of a reflector deviceand are connected between the surface of the reflector device and theinterior surface of the housing.

The connectors may comprise elasticized material strip connectorsadapted to maintain the surface of the reflector device in tension andmay preferably be in tension themselves.

The connectors may each be secured in position by engagement on one endwith a tab at the interior surface of the housing and at the oppositeend by a tab on the exterior surface of the reflector device.

A reflector embodying the invention is hereinafter described, by way ofexample, with reference to the accompanying drawing, which shows aschematic side elevational view, partly in phantom, of a reflector inthe form of a kite balloon.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the invention will now be described with reference to theaccompanying drawings in which:

FIG. 1 shows a reflector comprising a reflector device within aninflatable housing;

FIG. 2 is a perspective view of an exemplary reflector device;

FIG. 3 is a perspective view of one block of FIG. 2; and

FIG. 4 is a detail corresponding to FIG. 3 of an alternative embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a reflector 1 for incident electromagnetic energy, in thiscase in the radar range, comprising a hollow housing 2 in the form of aninflatable balloon and, interiorly thereof, a reflector device 3 forreflecting incident radar beams.

There are three reflector devices 3 in the balloon 2 in the embodimentshown. Each is substantially spherical and is made from an aluminizedcloth. The spheres 3 are maintained in tension, and thus spherical, by apositioning means comprised of elasticized strip material connectors 4such as elasticized cloth (only some of which are shown). The connectors4 extend over the whole surface area of the reflector device 3 and areconnected between tabs 5 at one end on the interior surface of thehousing 2 and at the opposite end by tabs 6 on the exterior surface ofthe spherical device 3. The tabs 5, 6 may comprise plastic or clothflaps with holes through which a hook carried by the ends of theconnectors 4 engage.

Only one set of tabs 5, 6 are shown for clarity. To manufacture thereflector 1 the material of the housing 2 is laid out as a sheet thetabs 5 are positioned as are the reflector devices 3 with the tabs 6 andthe connectors 4 are connected up to maintain the reflector devices 3 inposition. The material of the housing, suitably nylon coatedpolyurethane, is then folded so that opposite edges meet and these edgesare then heat welded together, leaving fins 7 intact and an inflationnozzle(s) 9 in place.

When the housing is inflated with air or helium, the reflector 1 can beflown in the air from the mast-head of a yacht. The reflectors 3 insidereflect incident radar energy so that the position of the yacht can beidentified. The configuration of the balloon 2 produces dynamic lift andthe fins 7 and rudder 8 provide dynamic stability. The rudder 8 keepsthe balloon heading into the wind and therefore provides a required"signature" whereby the identity of the yacht can be ascertained.

The reflector 1 may be tethered by suitable tethers 10.

The exemplary reflector device of FIG. 2 comprises eight identicalblocks. One block is shown in FIG. 3. The block is a regular cube withone corner bevelled away with the edges leading so that the corner isabout one fifth of the length of a full cube edge. The three remainingsquare sides of the cube are coated with aluminium, by any convenientmethod. The coating could alternatively be of a dielectric materialsince this also has reflecting properties for certain radiation. Theeight blocks are secured together, square face-to-square face, to form abody substantially sphere-shaped, as shown in FIG. 2. The metal coatingsare only exposed at their edges and this exposure can be protected byencapsulating the structure, for example in shrink wrap film or a moredurable plastic coating. A supporting member (not shown) can be affixedto the envelope of the encapsulation or secured in between two blocks,so that the reflector can be secured to another structure or attached toa cable.

The alternate embodiment of FIG. 4 shows the individual block as anexact eighth of a sphere. The quarter circle surfaces are metal coatedand secured together so that the full reflector is a sphere divided downthree mutually orthogonal planes by the metallic coating.

The blocks are made of any suitable lightweight material which does nothinder the passage of radiation. Conveniently, they can be foamedplastics material. The blocks are conveniently secured together byglueing the metallic surfaces. The metallic coating can be applied toone or (preferably) both of the facing surfaces between adjacent blocks.

The various aspects of the invention can be used singly or in anycombination.

I claim:
 1. A reflector for reflecting incident electromagnetic energy,comprising a hollow housing adapted to fly in ambient air and,interiorly thereof, a reflector device for reflecting incidentelectromagnetic radiation, said reflector device comprising aninflatable envelope and reflecting means within said envelope, andwherein the housing is inflatable with a suitable gas.
 2. A reflector asclaimed in claim 1 wherein the reflector device comprises asubstantially spherical device.
 3. A reflector as claimed in claim 2wherein the reflector device comprises an aluminized cloth which iselastic and formed into the shape of a sphere.
 4. A reflector as claimedin any one of claims 1 to 3 comprising means to position the reflectordevice interiorly of the housing.
 5. A reflector as claimed in claim 4wherein the positioning means comprises a plurality of separateconnectors which extend over substantially the whole surface of thereflector device and which are connected between that surface and theinterior surface of the housing.
 6. A reflector as claimed in claim 5wherein the connectors comprise elasticated material strip connectorswhich are adapted to maintain the surface of the reflector device intension.